The present invention relates to an apparatus and method for making dental models from which bridges, crowns, and other restorative dental work can be produced.
Restorative work plays a major part in dental care. Restorative measures such as crowns, bridges, and tooth protheses require the use of dental models from which to work. A dental model is typically made by a dentist's first creating a negative impression of the teeth. The negative impression is then filled with a casting material which hardens creating a model of the patient's teeth. In order to work on certain aspects of the model, the casting material must be sawed into usable segments.
Numerous inventions and devices have been devised to facilitate the dental model process. One example of the prior art includes U.S. Pat. No. 4,398,884 to Huffman, which describes an insert, which locks onto the casting material to guide each removal model tooth during insertion into and withdrawal from the dental model. A shortcoming of this art is that it is not possible to relate the maxillary and mandibular dental arches with one another in such a way as to recreate an accurate three-dimensional model showing the arches as they were at the time the mold was made. Another shortcoming of this art is that it requires multiple pours of casting material to create a base and a die.
Another apparatus for creating dental models is disclosed in U.S. Pat. No. 4,708,835, to Kiefer, wherein a base plate containing a plurality of pre-formed holes is fitted with dowel pins in each location where it is desired to make a die removable from a cast dental arch. Two methods of determining which of the pre-formed holes in a base plate are to have dowel pins inserted in them are disclosed. One version requires the use of a transparent datum plate which is positioned over the base plate and fitted with marker pins at desired locations. The data plate is then removed from the carrier plate, flipped over and remounted on the opposite side of the upright of the carrier plate. The base plate is then mounted to the upright of the carrier plate, over the data plate, and dowel pins are inserted into preformed holes in the base plate at those positions occupied by marker pins in the underlying data plate. Both datum plate and base plate with dowel pins inserted are then removed from the carrier plate, and the base plate is again flipped over and remounted to the opposite side of the carrier plate upright over a dental impression containing freshly poured liquid die stone, and pushed downward so the base plate contacts the impression.
In a second version, a transparent base plate having preformed blind holes on one side, and depressions on the opposite side of the plate aligned with the holes, for receiving colored marking ink, is placed over dental impression. Those depressions are locations where dowel pins are desired are then marked with ink and dowel pins inserted in the corresponding blind holes. This is a very complex procedure requiring extensive and unnecessary handling of the mold and casting material.
Another system, disclosed in U.S. Pat. No. 4,371,339 to Zeiser, requires the use of a complicated and expensive orienting apparatus which is has been manufactured to precise tolerances, for holding a dental impression while determining the locations on a prefabricated base plate where holes are subsequently to be made for securing dowel pins which will be molded into a dental arch.
Another method, disclosed in U.S. Pat. No. 4,439,151 to Whelan, describes a method to facilitate the mounting and dismounting of individual teeth by use of a central plastic insert member having projecting elements through the base of the tray to facilitate removal by pushing on said projection portions. The devise also incudes a means to pivot the trays apart to 180 degrees to provide pouring of both tray and impressions. A shortcoming of this art is that a model of only the mandibular or maxillary arch can be made. The model must then be removed from one member of the device and inserted into the second member before work on the model can be accomplished.